In recent years there has been increasing use of coated glass in the construction industry, especially in spandrel and interior design applications, since such glass is substantially less expensive than conventional exterior materials such as brick and granite and presents aesthetically appealing design choices for both exteriors and interiors. Metallic coatings have been applied by low temperature vacuum deposition and by high temperature pyrolitic methods in order to enhance both the aesthetic appeal and reflective character of such glass, the latter conserving energy in air-conditioned buildings. Ceramic frit coatings or so-called “ceramic enamels” have been used to color and to opacify pyrolitic metal-coated glass. However, ceramic frit coatings may not be used to coat glass that has been metal-coated by vacuum deposition because the approximately 1400° C. temperature required to apply the coatings distorts and melts the vacuum deposition metallic coating. Another drawback of the high temperature firing required to apply ceramic frit coatings is that it severely limits the number of color choices.
One recent attempt to overcome the problem of attempting to apply a ceramic frit coating over a vacuum-deposition metallic coating has been the development of a so-called “post-temperable” metallic-coated glass. This type of glass is prepared by applying an intermediate silicon layer over the metallic coating, curing the intermediate layer, then depositing the so-coated glass substrate in a tempering oven, whereupon the ceramic frit coating is then applied at an elevated temperature. The principal drawback of this procedure is that the temperature range that may be used to successfully apply the ceramic frit coating is very narrow.
The use of curable elastomeric silicone compositions for coating substrates such as steel and glass is known. See, for example, U.S. Pat. Nos. 3,889,023, 4,115,356, 4,163,081, 4,495,340 and 5,364,921. The use of such compositions for coating and reinforcement of architectural spandrel-type glass is also known. See commonly owned U.S. Pat. No. 4,814,230. There are a number of drawbacks of currently available elastomeric coatings for glass: they often are applied with solvents, thereby complicating application and lengthening curing times; many contain volatile organic compounds (VOCs), requiring measures to protect both workers and the environment; many are chemically unstable at higher temperatures; they usually have a relatively short shelf life; and, perhaps most importantly, they have insufficient adherence to meet four-sided structural glazing specifications.
There is therefore a need in the industry for a glass coating that enhances the tensile strength of all types of construction or architectural grade glass, that can render the same opaque and impart a large spectrum of colors thereto, that has a very rapid curing time, that has no VOCs and a 100% solids content, that can withstand the elements, that is chemically stable at higher temperatures, that has a long shelf life, that bonds to either glass substrates or to the metallic-coated side of glass substrates sufficiently to meet four-sided structural glazing specifications and that may be applied and cured at relatively cool temperatures so as not to distort or melt the metallic coating on glass. These needs are met by the present invention, which is summarized and described in detail below.